Valid built-in object types are:
o_fire - a fire which hurts players
o_supply - a supply crate (for non random content: PARAMETER = return value of addweapon)
o_mine - a mine which explodes when a player is close
o_beartrap - a trap
o_medikit - a medikit which heals you
o_node - a node (typically created in the editor only for mission scripting, invisible)
o_item - creates an item (PARAMETER = return value of addweapon)

Moreover you can use IDs returned by the addobject-command. This allows you to create and use your own custom objects.

It is recommended to use the Lua table "objects" as an array to store your custom object data. The array index is the ID of the object. Carnage Contest will reset this table each time a game is started.
Example:
objects[id].myvariable

Attention: This command does NOT return the ID of the new object!
Instead it calls the Lua setup-function of the object (if it is a custom object). It also passes the new ID and the PARAMETER:
setup(ID,PARAMETER)